[GreenAssailant]

BH3 <-- Boron trihydride
If you are to draw a Lewis structure, you would see that just a single bond is needed b/ween each B-H bond. Is Boron coordinate covalent bonding in this situation?

Also, its electron configuration before bonding is 1s^2 2s^2 2p^1
After bonding with those 3 Hydrogens, is its valence configuration going to be:

1s^2 2s^0 2p^0 OR

Does it hybridize and we get:

[e-, ][e-, ][e-, ] <--- sp^2 [e-, ] <--- p

What I am not understanding is how does Boron's valence configuration change before bonding versus after bonding?

[JustinCh3m]

what you said here about the free boron atom is correct:

its electron configuration before bonding is 1s^2 2s^2 2p^1

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when it's bonded, you need to consider the electron configuration as BH3 "as a whole".  Look up "Bonding in Heteronuclear Molecules" and read up on "Molecular Orbital Diagrams" in your G-chem text.

In GENERAL, electron configurations for MOLECULES look something like:

(sigma2s)^2(sigma*2s)^2(...)and so on -- look for something like this in your text.

PS - might want to read the bit about "p-s mixing" as well.  Shows up on quizzes/exams quite a bit.